The present invention relates to a binderless storage phosphor screen with vapour deposited phosphors.
A well known use of storage phosphors is in the production of X-ray images. In U.S. Pat. No. 3,859,527 a method for producing X-ray images with a photostimulable phosphor, which are incorporated in a panel is disclosed. The panel is exposed to incident pattern-wise modulated X-ray beam and as a result thereof the phosphor temporarily stores energy contained in the X-ray radiation pattern. At some interval after the exposure, a beam of visible or infra-red light scans the panel to stimulate the release of stored energy as light that is detected and converted to sequential electrical signals which (are) be processed to produce a visible image. For this purpose, the phosphor should store as much as possible of the incident X-ray energy and emit as little as possible of the stored energy until stimulated by the scanning beam. This is called xe2x80x9cdigital radiographyxe2x80x9d or xe2x80x9ccomputed radiographyxe2x80x9d.
Since in the above described X-ray recording systems the X-ray conversion screens are used repeatedly, it is important to provide them with an adequate topcoat for protecting the phosphor containing layer from mechanical and chemical damage. This is particularly important for photostimulable radiographic screens where screens are often transported in a scanning modulexe2x80x94wherein the stimulation of the stored energy takes placexe2x80x94while not being not encased in a cassette but is used and handled as such without protective encasing.
A protective layer can be coated onto the phosphor containing layer by directly applying thereto a coating solution containing a film-forming organic solvent-soluble polymer such as nitrocellulose, ethylcellulose or cellulose acetate or poly(meth)acrylic resin and removing the solvent by evaporation. According to another technique a clear, thin, tough, flexible, dimensionally stable polyamide film is bound to the phosphor layer as described in published EP-A-392 474.
According to a further known technique a protective overcoat is produced with a radiation-curable composition. Use of a radiation curable coating as protective top layer in a X-ray conversion screen is described e.g. in EP-A-209 358 and JP-A-86 176 900 and U.S. Pat. No. 4,893,021. For example, the protective layer comprises a UV cured resin composition formed by monomers and/or prepolymers that are polymerized by free-radical polymerisation with the aid of a photoinitiator. The monomeric products are preferably solvents for the prepolymers used.
In U.S. Pat. No. 6,120,902 an intensifying screen is disclosed carrying a radiation cured protective layer and having a determined unevenness. In U.S. Pat. No. 4,059,768 the use of polymeric beads containing fluoro-moieties in intensifying screens is disclosed so as to have screens with good transportability. In U.S. Pat. No. 5,401,971 storage phosphor screens are disclosed comprising a protective layer coated from a solution in butanone of a miscible blend of poly(vinylidene fluoride-co-tetrafluoroethylene) and poly(1 to 2 carbonalkyl) methacrylate.
Although all screens disclosed in this prior art can yield X-ray images with good quality, there is still a need for storage phosphor screens with increased physical strength that can be transported in scanner without risk of jamming, can withstand the wear and the tear of transporting and present no or low risk of electrical charging.
It is an object of the invention to provide a binderless stimulable phosphor screen useful in an X-ray recording system with a strong protective layer and that can be transported easily through a scanning module without causing jamming.
The above mentioned object is realized by providing a stimulable phosphor screen having the specific features defined in claim 1. Specific features for preferred embodiments of the invention are disclosed in the dependent claims.
Further advantages and embodiments of the present invention will become apparent from the following description and drawings.